The diversity of allowing theocracies isn't one I am particularly interested in supporting.

Whatever "true diversity" is it's not worth having unless _people_ can choose their own values to some extent, IMO.

Fascist cultures should not be tolerated, fascist people should (inasmuch as their fascism does not impact others against those other's own wills, of course).

Demanding SA allow freedom for individuals to exercise their own conscience would be supporting a morally defensible notion of diversity.

One major problem is that some religions (eg Islam) and religious groups (eg Mormons) have central ideologies that are antithetical to freedom of conscience; making them incompatible with many freedoms associated with democratic societies (speech, thought, association).

That's just another way of saying "you should tolerate intolerance", and the fallacy is the same.

Saudi Arabia and China are not cultural monoliths. Their ruling classes may have a cultural value of stamping out dissenting values, but their subcultures so targeted would certainly disagree.

In much of MENA, female genital mutilation is a cultural norm.

Are you saying that “true diversity” is allowing small girls to have their clitorises cut off?

So, true diversity in your opinion requires that we allow some king to torture and kill people who are too diverse?